To the Editor: We commend the retrospective survey of antimicrobial
susceptibility at 3 Military Hospital in Bloemfontein (1) and appreciate
the concern about very high rates of culture-negative urine received at
the laboratory. Possibly many such samples came from patients already
receiving antimicrobials. We feel that it would have been better to
screen urine samples received for culture for the presence of any
antimicrobials in the sample to ensure judicious therapeutic
intervention.

Recently, investigators at the Hamad Medical Corporation, Doha,
Qatar, carried out antibiotic screening of 1 680 urine samples
(employing Escherichia coli ATCC 25922 and Staphylococcus aureus ATCC
25923) that were being processed for culture. There were 2 494
culture-positive urine samples that included 388 samples with
antibacterial substances. Among these samples were 345 sterile samples,
32 with insignificant growth samples, and 11 with mixed growth. (2)

Screening urine samples received at 3 Military Hospital in
Bloemfontein (1) would not be an insurmountable task. Antibacterial
substance screening of urine samples was feasible even more than 40
years ago at the All India Institute of Medical Sciences, New Delhi,
India,3 where screening of 426 urine samples was done by employing the
standard Oxford strain of S. aureus. There was demonstrable
antibacterial activity in 127 samples, accompanied by bacterial growth
in 63 samples. Isolates included E. coli--28 isolates, Klebsiella
species--13, Pseudomonas aeruginosa--10, Proteus spp.--6, S. aureus --3,
Alkaligenes faecalis--2, and Streptococcus faecalis--1. A history of
prior antibiotic use could be obtained in 25 cases only, though there
was no relevant information in the laboratory requisition slips. It was
also possible in 7 cases to identify the antibiotics being used by the
patients. The isolates in the urine samples were resistant in vitro to
the prescribed antibiotics. Even with an adequate amount of antibiotic
in the urine, there was little benefit to the individual.

Obviously, any sterile culture report on a urine sample from a
patient with a demonstrable antibacterial activity could be erroneous
unless a subsequent urine culture is found to be sterile. Laboratory
personnel would not ignore patients with rather low bacterial counts in
any urine sample with concurrent antibacterial activity. Such isolates
might represent either a declining population of susceptible bacteria or
an ascending antibiotic-resistant bacteria population.

Last but not least, any expenditure for carrying out concurrent
screening for antibacterial substances in all urine samples cultured at
3 Military Hospital in Bloemfontein (1) or elsewhere would be
cost-effective, and will lead to better management of urinary tract
infections and would ensure rational disease management.

Dr van Vuuren replies: All urine samples included in our study were
processed by the National Health Laboratories Services (NHLS) in
Bloemfontein. In line with standard procedure, Bacillus subtilis ATCC
6633 was used to screen for the presence of antibiotics, and a leukocyte
count performed on all urine samples sent for culture at the NHLS. If
there is no growth of bacteria in the presence of antibiotics,
significant numbers of leukocytes warrant further investigation.

As we excluded culture-negative samples from our analysis, we
obviously cannot comment on the number of samples with no growth due to
the presence of antibiotics. Apart from the possibilities mentioned in
our article, antibiotic administration prior to sample collection may be
another cause for negative cultures.